cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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tty_buffer.c (16577B)


      1// SPDX-License-Identifier: GPL-2.0
      2/*
      3 * Tty buffer allocation management
      4 */
      5
      6#include <linux/types.h>
      7#include <linux/errno.h>
      8#include <linux/tty.h>
      9#include <linux/tty_driver.h>
     10#include <linux/tty_flip.h>
     11#include <linux/timer.h>
     12#include <linux/string.h>
     13#include <linux/slab.h>
     14#include <linux/sched.h>
     15#include <linux/wait.h>
     16#include <linux/bitops.h>
     17#include <linux/delay.h>
     18#include <linux/module.h>
     19#include <linux/ratelimit.h>
     20#include "tty.h"
     21
     22#define MIN_TTYB_SIZE	256
     23#define TTYB_ALIGN_MASK	255
     24
     25/*
     26 * Byte threshold to limit memory consumption for flip buffers.
     27 * The actual memory limit is > 2x this amount.
     28 */
     29#define TTYB_DEFAULT_MEM_LIMIT	(640 * 1024UL)
     30
     31/*
     32 * We default to dicing tty buffer allocations to this many characters
     33 * in order to avoid multiple page allocations. We know the size of
     34 * tty_buffer itself but it must also be taken into account that the
     35 * buffer is 256 byte aligned. See tty_buffer_find for the allocation
     36 * logic this must match.
     37 */
     38
     39#define TTY_BUFFER_PAGE	(((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
     40
     41/**
     42 * tty_buffer_lock_exclusive	-	gain exclusive access to buffer
     43 * @port: tty port owning the flip buffer
     44 *
     45 * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
     46 * the buffer work and any pending flush from using the flip buffer. Data can
     47 * continue to be added concurrently to the flip buffer from the driver side.
     48 *
     49 * See also tty_buffer_unlock_exclusive().
     50 */
     51void tty_buffer_lock_exclusive(struct tty_port *port)
     52{
     53	struct tty_bufhead *buf = &port->buf;
     54
     55	atomic_inc(&buf->priority);
     56	mutex_lock(&buf->lock);
     57}
     58EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
     59
     60/**
     61 * tty_buffer_unlock_exclusive	-	release exclusive access
     62 * @port: tty port owning the flip buffer
     63 *
     64 * The buffer work is restarted if there is data in the flip buffer.
     65 *
     66 * See also tty_buffer_lock_exclusive().
     67 */
     68void tty_buffer_unlock_exclusive(struct tty_port *port)
     69{
     70	struct tty_bufhead *buf = &port->buf;
     71	int restart;
     72
     73	restart = buf->head->commit != buf->head->read;
     74
     75	atomic_dec(&buf->priority);
     76	mutex_unlock(&buf->lock);
     77	if (restart)
     78		queue_work(system_unbound_wq, &buf->work);
     79}
     80EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
     81
     82/**
     83 * tty_buffer_space_avail	-	return unused buffer space
     84 * @port: tty port owning the flip buffer
     85 *
     86 * Returns: the # of bytes which can be written by the driver without reaching
     87 * the buffer limit.
     88 *
     89 * Note: this does not guarantee that memory is available to write the returned
     90 * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
     91 * guarantee is required).
     92 */
     93unsigned int tty_buffer_space_avail(struct tty_port *port)
     94{
     95	int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
     96
     97	return max(space, 0);
     98}
     99EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
    100
    101static void tty_buffer_reset(struct tty_buffer *p, size_t size)
    102{
    103	p->used = 0;
    104	p->size = size;
    105	p->next = NULL;
    106	p->commit = 0;
    107	p->read = 0;
    108	p->flags = 0;
    109}
    110
    111/**
    112 * tty_buffer_free_all		-	free buffers used by a tty
    113 * @port: tty port to free from
    114 *
    115 * Remove all the buffers pending on a tty whether queued with data or in the
    116 * free ring. Must be called when the tty is no longer in use.
    117 */
    118void tty_buffer_free_all(struct tty_port *port)
    119{
    120	struct tty_bufhead *buf = &port->buf;
    121	struct tty_buffer *p, *next;
    122	struct llist_node *llist;
    123	unsigned int freed = 0;
    124	int still_used;
    125
    126	while ((p = buf->head) != NULL) {
    127		buf->head = p->next;
    128		freed += p->size;
    129		if (p->size > 0)
    130			kfree(p);
    131	}
    132	llist = llist_del_all(&buf->free);
    133	llist_for_each_entry_safe(p, next, llist, free)
    134		kfree(p);
    135
    136	tty_buffer_reset(&buf->sentinel, 0);
    137	buf->head = &buf->sentinel;
    138	buf->tail = &buf->sentinel;
    139
    140	still_used = atomic_xchg(&buf->mem_used, 0);
    141	WARN(still_used != freed, "we still have not freed %d bytes!",
    142			still_used - freed);
    143}
    144
    145/**
    146 * tty_buffer_alloc	-	allocate a tty buffer
    147 * @port: tty port
    148 * @size: desired size (characters)
    149 *
    150 * Allocate a new tty buffer to hold the desired number of characters. We
    151 * round our buffers off in 256 character chunks to get better allocation
    152 * behaviour.
    153 *
    154 * Returns: %NULL if out of memory or the allocation would exceed the per
    155 * device queue.
    156 */
    157static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
    158{
    159	struct llist_node *free;
    160	struct tty_buffer *p;
    161
    162	/* Round the buffer size out */
    163	size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
    164
    165	if (size <= MIN_TTYB_SIZE) {
    166		free = llist_del_first(&port->buf.free);
    167		if (free) {
    168			p = llist_entry(free, struct tty_buffer, free);
    169			goto found;
    170		}
    171	}
    172
    173	/* Should possibly check if this fails for the largest buffer we
    174	 * have queued and recycle that ?
    175	 */
    176	if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
    177		return NULL;
    178	p = kmalloc(sizeof(struct tty_buffer) + 2 * size,
    179		    GFP_ATOMIC | __GFP_NOWARN);
    180	if (p == NULL)
    181		return NULL;
    182
    183found:
    184	tty_buffer_reset(p, size);
    185	atomic_add(size, &port->buf.mem_used);
    186	return p;
    187}
    188
    189/**
    190 * tty_buffer_free		-	free a tty buffer
    191 * @port: tty port owning the buffer
    192 * @b: the buffer to free
    193 *
    194 * Free a tty buffer, or add it to the free list according to our internal
    195 * strategy.
    196 */
    197static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
    198{
    199	struct tty_bufhead *buf = &port->buf;
    200
    201	/* Dumb strategy for now - should keep some stats */
    202	WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
    203
    204	if (b->size > MIN_TTYB_SIZE)
    205		kfree(b);
    206	else if (b->size > 0)
    207		llist_add(&b->free, &buf->free);
    208}
    209
    210/**
    211 * tty_buffer_flush		-	flush full tty buffers
    212 * @tty: tty to flush
    213 * @ld: optional ldisc ptr (must be referenced)
    214 *
    215 * Flush all the buffers containing receive data. If @ld != %NULL, flush the
    216 * ldisc input buffer.
    217 *
    218 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
    219 */
    220void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
    221{
    222	struct tty_port *port = tty->port;
    223	struct tty_bufhead *buf = &port->buf;
    224	struct tty_buffer *next;
    225
    226	atomic_inc(&buf->priority);
    227
    228	mutex_lock(&buf->lock);
    229	/* paired w/ release in __tty_buffer_request_room; ensures there are
    230	 * no pending memory accesses to the freed buffer
    231	 */
    232	while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
    233		tty_buffer_free(port, buf->head);
    234		buf->head = next;
    235	}
    236	buf->head->read = buf->head->commit;
    237
    238	if (ld && ld->ops->flush_buffer)
    239		ld->ops->flush_buffer(tty);
    240
    241	atomic_dec(&buf->priority);
    242	mutex_unlock(&buf->lock);
    243}
    244
    245/**
    246 * __tty_buffer_request_room	-	grow tty buffer if needed
    247 * @port: tty port
    248 * @size: size desired
    249 * @flags: buffer flags if new buffer allocated (default = 0)
    250 *
    251 * Make at least @size bytes of linear space available for the tty buffer.
    252 *
    253 * Will change over to a new buffer if the current buffer is encoded as
    254 * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
    255 * buffer.
    256 *
    257 * Returns: the size we managed to find.
    258 */
    259static int __tty_buffer_request_room(struct tty_port *port, size_t size,
    260				     int flags)
    261{
    262	struct tty_bufhead *buf = &port->buf;
    263	struct tty_buffer *b, *n;
    264	int left, change;
    265
    266	b = buf->tail;
    267	if (b->flags & TTYB_NORMAL)
    268		left = 2 * b->size - b->used;
    269	else
    270		left = b->size - b->used;
    271
    272	change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
    273	if (change || left < size) {
    274		/* This is the slow path - looking for new buffers to use */
    275		n = tty_buffer_alloc(port, size);
    276		if (n != NULL) {
    277			n->flags = flags;
    278			buf->tail = n;
    279			/* paired w/ acquire in flush_to_ldisc(); ensures
    280			 * flush_to_ldisc() sees buffer data.
    281			 */
    282			smp_store_release(&b->commit, b->used);
    283			/* paired w/ acquire in flush_to_ldisc(); ensures the
    284			 * latest commit value can be read before the head is
    285			 * advanced to the next buffer
    286			 */
    287			smp_store_release(&b->next, n);
    288		} else if (change)
    289			size = 0;
    290		else
    291			size = left;
    292	}
    293	return size;
    294}
    295
    296int tty_buffer_request_room(struct tty_port *port, size_t size)
    297{
    298	return __tty_buffer_request_room(port, size, 0);
    299}
    300EXPORT_SYMBOL_GPL(tty_buffer_request_room);
    301
    302/**
    303 * tty_insert_flip_string_fixed_flag - add characters to the tty buffer
    304 * @port: tty port
    305 * @chars: characters
    306 * @flag: flag value for each character
    307 * @size: size
    308 *
    309 * Queue a series of bytes to the tty buffering. All the characters passed are
    310 * marked with the supplied flag.
    311 *
    312 * Returns: the number added.
    313 */
    314int tty_insert_flip_string_fixed_flag(struct tty_port *port,
    315		const unsigned char *chars, char flag, size_t size)
    316{
    317	int copied = 0;
    318
    319	do {
    320		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
    321		int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
    322		int space = __tty_buffer_request_room(port, goal, flags);
    323		struct tty_buffer *tb = port->buf.tail;
    324
    325		if (unlikely(space == 0))
    326			break;
    327		memcpy(char_buf_ptr(tb, tb->used), chars, space);
    328		if (~tb->flags & TTYB_NORMAL)
    329			memset(flag_buf_ptr(tb, tb->used), flag, space);
    330		tb->used += space;
    331		copied += space;
    332		chars += space;
    333		/* There is a small chance that we need to split the data over
    334		 * several buffers. If this is the case we must loop.
    335		 */
    336	} while (unlikely(size > copied));
    337	return copied;
    338}
    339EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
    340
    341/**
    342 * tty_insert_flip_string_flags	-	add characters to the tty buffer
    343 * @port: tty port
    344 * @chars: characters
    345 * @flags: flag bytes
    346 * @size: size
    347 *
    348 * Queue a series of bytes to the tty buffering. For each character the flags
    349 * array indicates the status of the character.
    350 *
    351 * Returns: the number added.
    352 */
    353int tty_insert_flip_string_flags(struct tty_port *port,
    354		const unsigned char *chars, const char *flags, size_t size)
    355{
    356	int copied = 0;
    357
    358	do {
    359		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
    360		int space = tty_buffer_request_room(port, goal);
    361		struct tty_buffer *tb = port->buf.tail;
    362
    363		if (unlikely(space == 0))
    364			break;
    365		memcpy(char_buf_ptr(tb, tb->used), chars, space);
    366		memcpy(flag_buf_ptr(tb, tb->used), flags, space);
    367		tb->used += space;
    368		copied += space;
    369		chars += space;
    370		flags += space;
    371		/* There is a small chance that we need to split the data over
    372		 * several buffers. If this is the case we must loop.
    373		 */
    374	} while (unlikely(size > copied));
    375	return copied;
    376}
    377EXPORT_SYMBOL(tty_insert_flip_string_flags);
    378
    379/**
    380 * __tty_insert_flip_char   -	add one character to the tty buffer
    381 * @port: tty port
    382 * @ch: character
    383 * @flag: flag byte
    384 *
    385 * Queue a single byte @ch to the tty buffering, with an optional flag. This is
    386 * the slow path of tty_insert_flip_char().
    387 */
    388int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
    389{
    390	struct tty_buffer *tb;
    391	int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
    392
    393	if (!__tty_buffer_request_room(port, 1, flags))
    394		return 0;
    395
    396	tb = port->buf.tail;
    397	if (~tb->flags & TTYB_NORMAL)
    398		*flag_buf_ptr(tb, tb->used) = flag;
    399	*char_buf_ptr(tb, tb->used++) = ch;
    400
    401	return 1;
    402}
    403EXPORT_SYMBOL(__tty_insert_flip_char);
    404
    405/**
    406 * tty_prepare_flip_string	-	make room for characters
    407 * @port: tty port
    408 * @chars: return pointer for character write area
    409 * @size: desired size
    410 *
    411 * Prepare a block of space in the buffer for data.
    412 *
    413 * This is used for drivers that need their own block copy routines into the
    414 * buffer. There is no guarantee the buffer is a DMA target!
    415 *
    416 * Returns: the length available and buffer pointer (@chars) to the space which
    417 * is now allocated and accounted for as ready for normal characters.
    418 */
    419int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
    420		size_t size)
    421{
    422	int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
    423
    424	if (likely(space)) {
    425		struct tty_buffer *tb = port->buf.tail;
    426
    427		*chars = char_buf_ptr(tb, tb->used);
    428		if (~tb->flags & TTYB_NORMAL)
    429			memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
    430		tb->used += space;
    431	}
    432	return space;
    433}
    434EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
    435
    436/**
    437 * tty_ldisc_receive_buf	-	forward data to line discipline
    438 * @ld: line discipline to process input
    439 * @p: char buffer
    440 * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
    441 * @count: number of bytes to process
    442 *
    443 * Callers other than flush_to_ldisc() need to exclude the kworker from
    444 * concurrent use of the line discipline, see paste_selection().
    445 *
    446 * Returns: the number of bytes processed.
    447 */
    448int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
    449			  const char *f, int count)
    450{
    451	if (ld->ops->receive_buf2)
    452		count = ld->ops->receive_buf2(ld->tty, p, f, count);
    453	else {
    454		count = min_t(int, count, ld->tty->receive_room);
    455		if (count && ld->ops->receive_buf)
    456			ld->ops->receive_buf(ld->tty, p, f, count);
    457	}
    458	return count;
    459}
    460EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
    461
    462static int
    463receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
    464{
    465	unsigned char *p = char_buf_ptr(head, head->read);
    466	const char *f = NULL;
    467	int n;
    468
    469	if (~head->flags & TTYB_NORMAL)
    470		f = flag_buf_ptr(head, head->read);
    471
    472	n = port->client_ops->receive_buf(port, p, f, count);
    473	if (n > 0)
    474		memset(p, 0, n);
    475	return n;
    476}
    477
    478/**
    479 * flush_to_ldisc		-	flush data from buffer to ldisc
    480 * @work: tty structure passed from work queue.
    481 *
    482 * This routine is called out of the software interrupt to flush data from the
    483 * buffer chain to the line discipline.
    484 *
    485 * The receive_buf() method is single threaded for each tty instance.
    486 *
    487 * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
    488 */
    489static void flush_to_ldisc(struct work_struct *work)
    490{
    491	struct tty_port *port = container_of(work, struct tty_port, buf.work);
    492	struct tty_bufhead *buf = &port->buf;
    493
    494	mutex_lock(&buf->lock);
    495
    496	while (1) {
    497		struct tty_buffer *head = buf->head;
    498		struct tty_buffer *next;
    499		int count;
    500
    501		/* Ldisc or user is trying to gain exclusive access */
    502		if (atomic_read(&buf->priority))
    503			break;
    504
    505		/* paired w/ release in __tty_buffer_request_room();
    506		 * ensures commit value read is not stale if the head
    507		 * is advancing to the next buffer
    508		 */
    509		next = smp_load_acquire(&head->next);
    510		/* paired w/ release in __tty_buffer_request_room() or in
    511		 * tty_buffer_flush(); ensures we see the committed buffer data
    512		 */
    513		count = smp_load_acquire(&head->commit) - head->read;
    514		if (!count) {
    515			if (next == NULL)
    516				break;
    517			buf->head = next;
    518			tty_buffer_free(port, head);
    519			continue;
    520		}
    521
    522		count = receive_buf(port, head, count);
    523		if (!count)
    524			break;
    525		head->read += count;
    526
    527		if (need_resched())
    528			cond_resched();
    529	}
    530
    531	mutex_unlock(&buf->lock);
    532
    533}
    534
    535/**
    536 * tty_flip_buffer_push		-	push terminal buffers
    537 * @port: tty port to push
    538 *
    539 * Queue a push of the terminal flip buffers to the line discipline. Can be
    540 * called from IRQ/atomic context.
    541 *
    542 * In the event of the queue being busy for flipping the work will be held off
    543 * and retried later.
    544 */
    545void tty_flip_buffer_push(struct tty_port *port)
    546{
    547	struct tty_bufhead *buf = &port->buf;
    548
    549	/*
    550	 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
    551	 * buffer data.
    552	 */
    553	smp_store_release(&buf->tail->commit, buf->tail->used);
    554	queue_work(system_unbound_wq, &buf->work);
    555}
    556EXPORT_SYMBOL(tty_flip_buffer_push);
    557
    558/**
    559 * tty_buffer_init		-	prepare a tty buffer structure
    560 * @port: tty port to initialise
    561 *
    562 * Set up the initial state of the buffer management for a tty device. Must be
    563 * called before the other tty buffer functions are used.
    564 */
    565void tty_buffer_init(struct tty_port *port)
    566{
    567	struct tty_bufhead *buf = &port->buf;
    568
    569	mutex_init(&buf->lock);
    570	tty_buffer_reset(&buf->sentinel, 0);
    571	buf->head = &buf->sentinel;
    572	buf->tail = &buf->sentinel;
    573	init_llist_head(&buf->free);
    574	atomic_set(&buf->mem_used, 0);
    575	atomic_set(&buf->priority, 0);
    576	INIT_WORK(&buf->work, flush_to_ldisc);
    577	buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
    578}
    579
    580/**
    581 * tty_buffer_set_limit		-	change the tty buffer memory limit
    582 * @port: tty port to change
    583 * @limit: memory limit to set
    584 *
    585 * Change the tty buffer memory limit.
    586 *
    587 * Must be called before the other tty buffer functions are used.
    588 */
    589int tty_buffer_set_limit(struct tty_port *port, int limit)
    590{
    591	if (limit < MIN_TTYB_SIZE)
    592		return -EINVAL;
    593	port->buf.mem_limit = limit;
    594	return 0;
    595}
    596EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
    597
    598/* slave ptys can claim nested buffer lock when handling BRK and INTR */
    599void tty_buffer_set_lock_subclass(struct tty_port *port)
    600{
    601	lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
    602}
    603
    604bool tty_buffer_restart_work(struct tty_port *port)
    605{
    606	return queue_work(system_unbound_wq, &port->buf.work);
    607}
    608
    609bool tty_buffer_cancel_work(struct tty_port *port)
    610{
    611	return cancel_work_sync(&port->buf.work);
    612}
    613
    614void tty_buffer_flush_work(struct tty_port *port)
    615{
    616	flush_work(&port->buf.work);
    617}